The history
of water filtration has been an issue that has occupied people regarding engineering and medicine for
millennia. Among the earliest people to tackle the problem were the ancient
Indians and Egyptians. Alongside them was Hippocrates, who pioneered the use of
the Hippocratic sleeve – a cloth bag that water could be poured through after being boiled to help treat his patients.

Today, water
filtration is an exact science and remains an issue that occupies large amounts
of scientific ingenuity. After all, the quality of the water we use is
inescapably important. It is crucial to homes, communities, and whole
industries.

That being
the case, there are many approaches to ensuring water quality and purity,
ranging from the mechanical sieve-like approach pioneered by Hippocrates to
industrial-scale chemical scrubbing for harmful substances and residue.
However, one of the most common methods of water filtration for sediment in
homes is the use of string wound water
filters. But what
exactly are string wound water filters?

String Wound Water Filters Construction and
Application

As the name
suggests, string wound water filters consist of a central cartridge wrapped in
string. The string varies in thickness by layer, so the outer layer can trap
the largest particles, getting progressively thinner to the center, which
provides the overall rating (e.g. 5 micron)
of the filter.

String wound
water filters are a type of depth filter which is a filter that catches dirt
not just on its surface, but the whole way down to its core. It is important to
remember that string wound filters are exclusively sediment filters. They
physically trap dirt and sediment from the water, and, therefore, they are not
suitable for filtering chemicals or altering the taste of the water.

String wound
water filters date back a long time. The first to be sold in the U.S. was in
the mid-1930s. It was made of a woven
wire mesh wrapped in cotton yarn, which was
wrapped in a diamond pattern. The corners of the diamond shapes were the
main points at which dirt would be trapped,
rather than filtering sediment the whole way through the structure.

Later, in
the 1960s and ‘70s, string wound filters began to rise in popularity. This was partly due to the increase in the use of polypropylene core and other synthetic fabrics, which
were preferred to cotton as they were resistant to the growth of microorganisms
and could be treated to be compatible with or resistant to various chemicals.
This generation of string wound filters normally used rovings rather than
traditional yarns. These were partially twisted
rolls or strands of fibers that were more cost-effective and normally extended
the life of the filter, as they allowed more water to pass through.

Later, the
rovings were generally replaced by
friction-spun yarns. These are comparatively bulky and have less resistance to
flow, which helps to further increase the performance life of the water filter.
However, the treatment process for the fibers used in both rovings and
friction-spun yarns can result in some chemicals leaching into the water, and
the short length of the fibers means they are prone to being displaced, which limits the performance of the filter.

String Wound Filters Today

More
recently, string wound water filters have been
produced according to a different method, where, rather than using shorter
fibers, single continuous filaments are used that run the length of the
cartridge and are carefully wound together. This method involves melt-spun
fibers, which are free from the chemical treatment process used in rovings and
friction-spun styles. Also, the
arrangement of the fibers is extremely stable, as they are randomly oriented
and are produced with short loops
protruding from their surfaces. When they are
wound together, these loops trap one another, helping to enmesh the
fibers and prevent them from being dislodged. The
use of computers in designing the arrangement also means the distance between
the yarns can be carefully controlled, which helps to fine-tune the filtering
capabilities and microns of the outer layers versus the inner ones, which
provides an effective solution for improving the performance of the filter
overall and ensuring the separate layers function as intended.

Conclusion

String wound
water filters are a common and extremely effective choice in many contexts, and
the more recent designs have further
increased their efficacy over what was already a reliable and cost-effective
design. In the vast majority of cases, they are an effective choice for any
residence or business.